1. Field of the Invention
The present invention is directed to an optical display or indicating device which utilizes a liquid crystal cell having a liquid crystal layer which is zonally switchable between different optical conditions by segmented electrodes which are disposed on inner surfaces of the carrier plates forming the cell. The device includes a fluorescent plate, which is disposed behind a liquid crystal cell in relation to the direction of viewing and which consists of a material with an index of refraction greater than 1 and contains fluorescent centers to produce fluorescent light.
2. Prior Art
A display, which has a high contrast between the symbols or image being displayed and the background light and includes a fluorescent plate which contains a plurality of fluorescent centers, has been proposed in German patent application No. P 25 54 226, whose disclosure was included in United States patent application Ser. No. 747,035 filed on Dec. 2, 1976. In the proposed device, a large part of the ambient light, which impinges upon the fluorescent plate, is held within the plate by transformation at the fluorescent centers and due to subsequent total reflection of the transformed or fluorescent light. The fluorescent light is finally passed out of the plate through light emergent or exit windows through a liquid crystal cell with a relatively high light intensity. With a large ratio of the light collecting area of the plate to the area of the light emitting or exit windows, the intensity of the light passing through the switchable zones of the liquid crystal cell has a greater intensity in relation to the light intensity of the background area. In the proposed cells of the German application, the fluorescent plate would extend laterally beyond the actual area of the cell and always contains the decoupling light exit window in the form of silvered notched that were aligned with the segment electrodes. The liquid crystal cell was a so-called "rotary cell" or "twisted nematic cell" which was provided with polarizers.
The above mentioned U.S. application suggested using a dynamic scattering cell with polarizers, and one embodiment utilized a dynamic scattering cell without polarizing to partially decouple the light from the display. However, this cell required either an additional fluorescent screen or diffusing plate in order to render the decoupled light visible to the viewer.